1. Field of the Invention
A compliant trim for use between concrete slabs is the subject of this invention. It is intended for the repair and replacement of wood commonly used as formwork to divide concrete slabs during their installation.
2. Description of Prior Art
In residential construction of driveways and sidewalks, wood is typically used for the formwork. This formwork is often left between individual slabs after the external formwork is removed. The wood is subject to rot and decay, even if a rot-resistant variety is used such as cedar. Additionally, the wood holds moisture and collects dirt and debris in the space between the wood and the concrete, leading to weed growth between the slabs. This condition requires repeated application of weed-killing chemicals, and makes the concrete joint vulnerable to freeze-thaw cycles.
Current art replaces rotted or damaged wood formwork with a viscous liquid sealant that hardens to a rubber-like consistency. Such a material is disclosed by Frandina, U.S. Pat. No. 5,116,653. This type of material is typically sold in tubes which are dispensed by hand chalk gun into a joint that has been cleared of the wood formwork. This repair method is labor-intensive, messy, costly, and the finished product is greatly dependent on the skill of the installer. The quantity of sealant needed for a given job is also difficult to assess in advance, as the volume of the cavity between the slabs is difficult to determine. This often results in repeat visits to the point of purchase, either for the purchase of additional quantities, or the return of unused product. Additionally, this method must cure, and it must remain undisturbed for some time before its final properties are developed.
Another approach to this problem in the current art seeks to plug this gap with a preformed compliant material. Gibbon et al, U.S. Pat. No. 4,699,540, disclose a compliant tube-shaped element which is anchored with a liquid sealant. This method requires a specific shape be present in the slab edges. This shape is not typically cast into slab edges; it can be created, however, if specific material is removed to form the appropriate cavity for installation. This amount of preparation makes this prohibitively expensive for the repair and replacement of residential driveways and sidewalks due to the equipment and labor required to cut and remove cured concrete. This method also has the same disadvantages as pure liquid sealants, in that it will be potentially messy and it's final appearance dependent on the skill of the installer.
Corrie, U.S. Pat. No. 5,888,017, discloses a compliant sealing element intended for interior flooring which can be placed in a simple gap. While avoiding the complexity of Gibbon et al, this expansion joint cap is proud of the surface, and as such, must be made sufficiently strong to accommodate the automobile and foot traffic without accumulating damage. It must also be thin enough to avoid becoming a trip hazard. These competing needs make the material selection rather difficult for the application of repairing driveways. Additionally, the expansion joint cap is designed for application on slab edges without significant edge radii. Residential driveways typically have an edges radius around each slab.
The current art also includes a hollow trapezoidal section fabricated from extruded vinyl. While the trapezoidal cross-section is expressly intended for the repair of driveways and sidewalks, the trapezoidal cross-section has several limitations. The trapezoidal cross section is difficult to install and maintain to a consistent depth, requiring that the joint be filled with sand or other filler material prior to the installation of the trapezoidal section. The trapezoidal cross-section also has limited compliance to variations in joint width, which increases the effort of installation and may necessitate the use of several different extrusion widths to accommodate variations found in typical installations. Additionally, the amount of material used to produce this cross-section is inefficient, making the weight and bulk of the raw material difficult to handle.
The current art has a common susceptibility to weed and plant growth. This susceptibility stems from a very low volume vertical space between the expansion joint material and the slab. In the case of liquid sealants, this space is formed when the cured sealant delaminates from the slab, either due to poor adhesion, shrinkage of the sealant, or excessive motion of the slabs tending to increase the gap beyond the capability of the sealant to comply. In the case of wooden expansion joints, this condition exists from the moment of installation. This space is filled relatively quickly with particulate, and is exploited by plant roots to access moisture below the expansion joint. Because the surface of the slab is rough and sealing cannot be relied upon, inventions such as Wangerow et al, U.S. Pat. No. 3,521,528, and Nicholas, U.S. Pat. No. 4,522,413 illustrate a geometry with little volume between the expansion joint material and the slab. These small gaps will quickly fill with particulate, and these inventions are therefore poor for the purpose of inhibiting plant/weed growth.